The contamination of subsurface soils and groundwater by volatile organic compounds (VOCs), semi volatile organic compounds (SVOCs) as well as herbicides and pesticides is a well-documented problem. Many VOC and SVOC contaminates migrate through soil under the influence of gravity to contaminate groundwater as the water passes through the contaminated soil. Notable among these are the volatile organic compounds or VOCs which include any at least slightly water soluble chemical compound of carbon, with a Henry's Law Constant greater than 10.sup.-7 atm m.sup.3/mole, which is toxic or carcinogenic, is capable of moving through the soil under the influence of gravity and serving as a source of water contamination by dissolution into water passing through the contaminated soil due to its solubility, including, but not limited to, chlorinated solvents such as trichloroethylene (TCE), vinyl chloride, tetrachloroethylene (PCE), methylene chloride, 1,2-dichloroethane, 1,1,1-trichloroethane (TCA), 1,1-dichloroethane, 1,1-dichloroethene, carbon tetrachloride, benzene, chloroform, chlorobenzenes, and other compounds such as ethylene dibromide, and methyl tertiary butyl ether.
Many VOC and SVOC contaminates also are toxic or carcinogenic. These VOCs and SVOC's contaminates include, but are not limited to, chlorinated solvents such as trichloroethylene (TCE), vinyl chloride, tetrachloroethylene (PCE), methylene chloride, 1,2-dichloroethane, 1,1,1-trichloroethane (TCA), carbon tetrachloride, chloroform, chlorobenzenes. Other examples of VOCs and SVOCs include benzene, toluene, xylene, ethyl benzene, ethylene dibromide, methyl tertiary butyl ether, polyaromatic hydrocarbons, polychlorobiphenyls, phthalates, 1,4-dioxane, nitrosodimethyl amine, and methyl tertbutyl ether.
The discharge of VOC and SVOC contaminates such as those listed into soil leads to contamination of aquifers and degrades groundwater resources for future use. Treatment and remediation of soils contaminated with VOCs or SVOCs is expensive and is often unsuccessful. For example, remediation of soils contaminated with VOCs which are partially or completely immiscible with water is particularly difficult. Also remediation of soils contaminated with highly soluble but biologically stable organic contaminants such as MTBE and 1,4-dioxane is very difficult with conventional technologies. Non-aqueous phase liquids (“NAPL”) present in the soil subsurface can be toxic and can slowly release dissolved VOCs to groundwater to generate long-term (i.e., decades or longer) sources of contamination of the soil subsurface. Indeed, plumes of subsurface groundwater contaminant may extend hundreds to thousands of feet from the source of the chemical contaminate. The chemical contaminates may then be transported into drinking water sources, lakes, rivers, and even basements of homes through volatilization from groundwater.
The art has attempted to address remediation of soil and groundwater contaminated with VOCs and SVOCs. U.S. Pat. No. 6,474,908 (Hoag, et al) and U.S. Pat. No. 6,019,548 (Hoag, et al) teach the use of persulfate with divalent transition metal salt catalyst to destroy VOC's in soil. A disadvantage of this technique, however, is that the divalent transition metals upon oxidation and/or hydrolysis may undergo precipitation. This limits the survivability and transport of the transition metal catalyst, and hence the reactivity of the persulfate to the field of contamination. Iron (III) is known to catalyze reactions of hydrogen peroxide. (Hydrogen Peroxide; Schumb, W. C; Satterfield, C. N.; and Wentworth, R. L; Reinhold Publishing Corporation, New York, N.Y., 1955; pg 469). Iron (III) complexes used with hydrogen peroxide show an ability to oxidize complex pesticides (Sun, Y and Pignatello, J. J. Agr. Food. Chem, 40:322-37, 1992). However Iron (III) is a poor catalyst for activation of persulfate.
The U.S. Environmental Protection Agency (USEPA) has established maximum concentration limits for various contaminate compounds. Very low and stringent limits on the amount of halogenated organic compounds in drinking water exist. For example, the maximum concentration of solvents such as trichloroethylene, tetrachloroethylene, and carbon tetrachloride in drinking water is 5 mu.g/L, and the maximum concentration of chlorobenzenes, polychlorinated biphenyls (PCBs), and ethylene dibromide are 100 mu.g/L, 0.5 mu./L, and 0.05 mu.g/L, respectively. Satisfying these limits during remediation of contaminated soils is often virtually impossible using existing technologies.
A need therefore exists for a method of remediation that overcomes the deficiencies of the prior art.